The Chez atom record gains watches (an alist of key->fn) and validator
slots. swap!/reset! now validate the candidate value before storing and
notify watches after, in the seed's order (core_refs.janet) — the watch fn
is called (key ref old new). compare-and-set!/swap-vals!/reset-vals! route
through reset!/swap! so they validate + notify too.
add-watch/remove-watch/set-validator!/get-validator are native here and
re-asserted in post-prelude.ss: the clojure.core overlay implements them via
jolt.host/ref-put! on (get atom :watches), a Janet-table mutation a Chez atom
record can't answer, so its def-var! would otherwise clobber these. set-
validator! validates the current value immediately (Clojure throws if already
invalid).
Parity 2150 -> 2154, 0 new divergences. New test/chez/_atomwatch.janet 10/10.
The (class x) native and the clojure.walk port were explored this increment
but deferred: class alone makes the String-class-token corpus cases emit-and-
run with a wrong value (the bare token doesn't resolve yet) — filed jolt-13zk
to land the native together with token resolution; clojure.walk is blocked on
list? + map-entry-as-vector (jolt-75sv).
